Pressure-regulating valves

ABSTRACT

A pressure-regulating valve includes a valve sleeve with first and second ends defining a longitudinal axis, a sense line, a sense piston, a main chamber, and first and second valve spools. The sleeve includes an axially aligned bore. The sense line is within the bore proximate the first end. The sense piston is within the bore between the sense line and the second end, and is configured to move along the longitudinal axis in response to pressure exerted by fluid in the sense line. The main chamber is within the bore between the sense piston and the second end, and includes supply and vent ports. The first valve spool is within the bore between the sense piston and the second end. The second valve spool is within the bore between the first valve spool and the second end.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to valves, and, in particular, topressure-regulating valves.

2. Description of Related Art

Traditional pressure-regulating valves can be used, for example, inhydraulic cooling circuits of an electrical generator. Generatorstypically include a rotor which is driven to rotate by a source ofrotation, such as a gas turbine engine on an aircraft. The rotor carrieselectric windings, which rotate in proximity to stator windings. Therotation of the rotor adjacent to the stator generates electricity.Cooling fluid is required to be delivered to several locations withinthe generator to ensure continued efficient operation of the systems andcomponents.

Traditional regulating valves can sometimes experience instabilitypotentially resulting in cooling circuit failures. Instability can arisefrom insufficient damping due to trapped air in chambers of the valve,and/or to incompatibility between the pressure-regulating valvefrequency response and the hydraulic circuit frequency response.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purposes. However, there is still a needin the art for systems and methods that allow for improved regulatingvalves. The present invention provides a solution for these problems.

SUMMARY OF THE INVENTION

A pressure-regulating valve includes a valve sleeve, a sense line, asense piston, a main chamber, and first and second valve spools. Thevalve sleeve includes first and second ends defining a longitudinal axistherebetween and a bore axially aligned between the first and secondends. The sense line is defined within the bore proximate the first endof the valve sleeve. The sense piston is mounted within the bore betweenthe sense line and the second end of the valve sleeve. The sense pistonis configured to move along the longitudinal axis in response topressure exerted by fluid in the sense line. The main chamber is definedwithin the bore between the sense piston and the second end and includessupply and vent ports. The supply port and the vent port are in fluidcommunication with one another by way of the main chamber. The firstvalve spool is mounted within the bore between the sense piston and thesecond end of the valve sleeve and occludes a portion of the vent portto a variable extent to modulate a flow rate between the supply port andthe vent port. The first valve spool is configured to move along thelongitudinal axis to modulate a flow rate in a fluid circuit forregulation of a sense pressure. The second valve spool is mounted withinthe bore between the first valve spool and the second end of the valvesleeve and is configured to move along the longitudinal axis to modulateflow rate in a bypass line for regulation of a balance pressure.

The valve sleeve can include first and second housing portions proximatethe first and second ends, respectively. The sense piston and firstvalve spool can be mounted in the first housing portion and the secondvalve spool can be mounted in the second housing portion. The secondhousing portion can be secured to the first housing portion with amechanical fastener.

The pressure-regulating valve can include a first spring mounted betweenthe first valve spool and the second housing portion. The first springcan be operatively connected to the first valve spool for biasing thefirst valve spool towards the first end of the valve sleeve. A secondspring can be mounted within the bore between the second valve spool andthe second end of the valve sleeve. The second spring can be operativelyconnected to the second valve spool for biasing the second valve spooltowards the first end of the valve sleeve.

The pressure-regulating valve can include a bypass line defined betweenthe sense line and a balance pressure chamber for fluid communicationtherebetween. The balance pressure chamber can be defined between thefirst and second valve spools and can include an inlet and an outlet.The second valve spool can occlude a portion of the outlet of thebalance pressure chamber to a variable extent to regulate pressurewithin the balance pressure chamber. The balance pressure chamber canform a portion of a balance pressure circuit and can be configured forcontinuous fluid flow between the inlet of the balance pressure chamberand the outlet of the balance pressure chamber for purging trapped airfrom the balance pressure circuit.

The main chamber can be defined between first and second land portionsof the first valve spool. The bypass line can be defined through thesense piston and/or the first valve spool. The pressure-regulating valvecan include a bypass orifice within a portion of the bypass line in thesense piston proximate to the sense line, and/or within a portion of thebypass line in the second land portion proximate the balance pressurechamber. The bypass orifice can be configured to sustain a pressuredifferential between the sense line and the balance pressure chamber andto meter flow through the bypass line. The pressure-regulating valve caninclude a transfer tube between the sense piston and the first landportion of the first valve spool for connecting a first portion of thebypass line in the sense piston with a second portion of the bypass linein the first valve spool. The bypass line can be defined between themain chamber and the balance pressure chamber for fluid communicationtherebetween.

A generator includes a housing, a rotor disposed in the housing, a fluidcircuit including an inlet and outlet port, and a pressure-regulatingvalve. The rotor is configured to rotate and generate electricity. Thepressure-regulating valve is operatively connected to the fluid circuitto modulate the flow of fluid through the fluid circuit so as toregulate pressure in the sense line. The sense line is in fluidcommunication with the fluid circuit. The supply and vent ports of themain chamber are in fluid communication with an oil pump disposed in thehousing of the generator. A frequency response of thepressure-regulating valve is configured to be tunable for compatibilitywith a frequency response of the fluid circuit.

These and other features of the systems and methods of the subjectinvention will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject inventionappertains will readily understand how to make and use the devices andmethods of the subject invention without undue experimentation,preferred embodiments thereof will be described in detail herein belowwith reference to certain figures, wherein:

FIG. 1 is a schematic plan view of a portion of an exemplary embodimentof a generator constructed in accordance with the present disclosure;

FIG. 2 is a cross-sectional side-elevation view of an exemplaryembodiment of a pressure-regulating valve constructed in accordance withthe present disclosure, showing the first valve spool and the firstspring, and the second valve spool and the second spring; and

FIG. 3 is a cross-sectional side-elevation view of another exemplaryembodiment of a pressure-regulating valve constructed in accordance withthe present disclosure, showing the bypass line defined between the mainchamber and the balance pressure chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, a perspective view of an exemplary embodiment of apressure-regulating valve in a generator in accordance with thedisclosure is shown in FIG. 1 and is designated generally by referencecharacter 100. Other embodiments of pressure-regulating valves inaccordance with the disclosure, or aspects thereof, are provided inFIGS. 2-3, as will be described.

As shown in FIG. 1, a generator 10 includes a housing 12, a rotor 14disposed in housing 12 including an inlet port 18 and an outlet port 20,a fluid circuit 16, a heat exchanger 17 in fluid communication withfluid circuit 16, and a pressure-regulating valve 100. Rotor 14 isconfigured to rotate and generate electricity. Pressure-regulating valve100 is operatively connected to fluid circuit 16 to regulate thepressure of fluid, such as cooling and/or lubricating oil, at inlet port18. Those skilled in the art will readily appreciate thatpressure-regulating valve 100 can be disposed in a variety of suitablelocations along fluid circuit 16. Arrows schematically show the fluidflow through fluid circuit 16.

With reference now to FIGS. 1 and 2, pressure-regulating valve 100includes a valve sleeve 102 with first and second ends 114 and 116,respectively, and a sense line 104. First and second ends 114 and 116,respectively, define a longitudinal axis A therebetween.Pressure-regulating valve 100 includes a bore 118 axially alignedbetween first and second ends, 114 and 116, respectively. Sense line 104is defined within bore 118 proximate first end 114 and is in fluidcommunication with fluid circuit 16. A main chamber 108 is definedwithin the bore of valve sleeve 102 and includes supply and vent ports,120 and 122, respectively. Supply and vent ports, 120 and 122,respectively, are in fluid communication with one another by way of mainchamber 108, and are in fluid communication with an oil pump 22. Ventport 122 outlets into a sump 24.

Now with reference to FIG. 2, pressure-regulating valve 100 includes asense piston 106, a first valve spool 110 and a second valve spool 112.Sense piston 106 is mounted within bore 118 between sense line 104 andfirst valve spool 110. Sense piston 106 is configured to move alonglongitudinal axis A in response to pressure exerted by fluid in senseline 104. First valve spool 110 is mounted within bore 118 between sensepiston 106 and a second housing portion 126 and occludes a portion ofvent port 122 to a variable extent to modulate a flow rate betweensupply port 120 and vent port 122. The modulation of flow rate throughmain chamber 108, between supply port 120 and vent port 122, is themeans for modulating flow rate through hydraulic cooling circuit, e.g.fluid circuit 16, for the purpose of regulating pressure at sense line104.

First valve spool 110 is configured to move along longitudinal axis A tomodulate a flow rate in fluid circuit 16 for regulation of a sensepressure. Second valve spool 112 is mounted within bore 118 betweenfirst valve spool 110 and second end 116 and is configured to move alonglongitudinal axis A to modulate flow rate in a bypass line 134 forregulation of a balance pressure. Those skilled in the art will readilyappreciate that the regulated balance pressure counteracts a sense forceexerted on first valve spool 110 by the sense pressure with a balanceforce. If the sense force and balance force are not in equilibrium,first valve spool 110 will translate, thus modulating flow rate fromsupply 120 to sump 24 until the sense force comes into equilibrium withthe balance force. A frequency bandwidth of pressure-regulating valve100 is tunable for avoiding frequency bandwidth incompatibility withfluid circuit 16, described above.

With continued reference to FIG. 2, valve sleeve 102 includes a firsthousing portion 124 proximate first end 114 and second housing portion126 proximate second end 116. Sense piston 106 and first valve spool 110are mounted in first housing portion 124, i.e. first stage regulator,and second valve spool 112 is mounted in second housing portion 126,i.e. second stage regulator. Alternatively, it is contemplated thatsense piston 106 can be mounted in first housing portion 124, whilefirst valve spool 110 and second valve spool 112 can be mounted insecond housing portion 126. Second housing portion 126 is secured tofirst housing portion 124 with a mechanical fastener 128.Pressure-regulating valve 100 includes a first spring 130 mountedbetween first valve spool 110 and second housing portion 126. Firstspring 130 is operatively connected to first valve spool 110 for biasingfirst valve spool 110 towards first end 114 of valve sleeve 102. Asecond spring 132 is mounted within bore 118 between second valve spool112 and second end 116. Second spring 132 is operatively connected tosecond valve spool 112 for biasing second valve spool 112 towards firstend 114 of valve sleeve 102.

As shown in FIG. 2, the bypass line 134 is defined between sense line104 and a balance pressure chamber 136, through the sense piston 106 andthe first valve spool 110, for fluid communication between sense line104 and balance pressure chamber 136. Balance pressure chamber 136 isdefined between the first and second valve spools, 110 and 112,respectively, and includes an inlet 135 and an outlet 137. It iscontemplated that second valve spool 112 can move between a fully openposition and an occluded position, where the occluded position variablyblocks at least a portion of outlet 137 of balance pressure chamber 136to modulate a flow rate between inlet 135 and outlet 137 of balancepressure chamber. Inlet 135 is defined where the balance pressurechamber 136 meets an end of the bypass line 134. Balance pressurechamber 136 forms a portion of a balance pressure circuit. Balancepressure circuit starts at sense line 104 and includes bypass line 134,and balance pressure chamber 136. Balance pressure chamber 136 isconfigured for continuous fluid flow between inlet 135 and outlet 137 toenable both negative and positive modulation of flow rate between inlet135 and outlet 137 and to purge trapped air from balance pressurechamber 136.

Those skilled in the art will readily appreciate that the reduction intrapped air tends to increase the stiffness of the fluid, thereinincreasing the dampening robustness of the fluid. Main chamber 108 isdefined between first and second land portions, 144 and 146,respectively, of first valve spool 110. It is contemplated that firstvalve spool 110 can move between a fully open position and an occludedposition, where the occluded position variably blocks at least a portionof vent port 122 to modulate a flow rate between supply port 120 andvent port 122.

Pressure-regulating valve 100 includes a bypass orifice 140 within aportion of the bypass line 134 in the sense piston 106 proximate to thesense line 104. Bypass orifice 140 is configured to sustain a pressuredifferential between the sense line and balance pressure chamber and tometer flow through the bypass line. Pressure-regulating valve 100includes a transfer tube 142 between sense piston 106 and a first landportion 144 of the first valve spool 110 for connecting a first portionof bypass line 134 in the sense piston 106 with a second portion ofbypass line 134 in the first valve spool 110. Transfer tube 142mitigates leakage to a chamber 107 surrounding sense piston 106.

Now with reference to FIG. 3, a pressure-regulating valve 200 includesfirst and second ends, 214 and 216, respectively, and a bore 218,similar to ends and bore described above with respect topressure-regulating valve 100. Pressure-regulating valve 200 includes avalve sleeve 202, a sense line 204, a sense piston 206, a main chamber208, a first valve spool 210, a second valve spool 212, a balancepressure chamber 236, a first spring 230 and a second spring 232, all ofwhich are similar to those described above with respect topressure-regulating valve 100.

With continued reference to FIG. 3, in pressure-regulating valve 200, abypass line 234 is defined between main chamber 208 and balance pressurechamber 236 for fluid communication therebetween. A bypass orifice 240,similar to bypass orifice 140 described above, is defined within aportion of bypass line 234 in second land portion 246 proximate balancepressure chamber 236. Those skilled in the art will readily appreciatethat a transfer tube, e.g. transfer tube 142, is not required inpressure-regulating valve 200 because bypass line 234 is only definedthrough first valve spool 210.

Now with reference to FIGS. 2 and 3, the overall control gain frequencyresponse function, G_(c)(s), for pressure-regulating valves 100 and 200,respectively, is in the form of a frequency-band-limitedproportional-action controller with lag compensator and is governed bythe following equation:

${G_{c}(s)} = \frac{K( {{\tau_{lead}s} + 1} )}{( {{\tau_{lag}s} + 1} )( {\frac{s^{2}}{\omega_{n}^{2}} + {\frac{2\zeta}{\omega_{n}}s} + 1} )}$wherein K is the proportional gain, ω_(n) is the natural frequency, andζ is the damping ratio of the band-limited proportional-actioncontroller. The time constants, τ_(lead) and τ_(lag), are the timeconstants associated with the lag compensator. The variable s representsthe Laplace variable.

Pressure regulating valves 100 and 200 produce control action inproportion to the difference between the sense force and the balanceforce, described above. The overall control gain is highest with value,K, at low frequencies having periods longer than the compensator lagtime constant, τ_(lag). The overall control gain, G_(c)(s),progressively attenuates over increasing frequencies having periodsbetween the lead and lag time constants, τ_(lead) and τ_(lag),respectively. At frequencies beyond τ_(lead), the overall control gainis level up to the band-limiting natural frequency, ω_(n). Atfrequencies beyond ω_(n), the overall control gain diminishes steeply.The result is a frequency-band-limited proportional-action controllerwith a lag compensator.

Those skilled in the art will readily appreciate that the frequency bandlimit tends to permit pressure regulating valves 100 and 200 to beconfigured to have diminished action at natural frequencies associatedwith the hydraulic cooling circuit, resulting in improved systemstability. It is also contemplated that the lag compensator tends topermit pressure regulating valves 100 and 200 to be configured to havelarge impact at very low frequencies thus resulting in very small steadystate error between the sense force and the balance force. The balanceforces of each balance chamber 136 and 236 plus forces of theirrespective first springs 130 and 230 establish the target value for aregulated pressure in a balance chamber.

With continued reference to FIGS. 2 and 3, pressure-regulating valves100 and 200 do not need to include their first springs 130 and 230,respectively. Those skilled in the art will readily appreciate that afirst spring, e.g. first spring 130 or 230, is optional. In the absenceof the first spring, a first valve spool, e.g. first valve spool 110 or210, moves continuously until the sense pressure force is in equilibriumwith the reaction force, e.g. balance force, induced by the regulatedpressure in a balance chamber, e.g. balance pressure chamber 136 or 236,of the second stage regulator. The overall frequency response function,G_(c)(s), for each of pressure-regulating valves 100 and 200, withouttheir respective first springs 130 and 230, is governed by the followingequation:

${G_{c}(s)} = \frac{K( {{\tau_{lead}s} + 1} )}{s( {\frac{s^{2}}{\omega_{n}^{2}} + {\frac{2\zeta}{\omega_{n}}s} + 1} )}$wherein K is the proportional gain, ω_(n) is the band-limit naturalfrequency, and ζ is the damping ratio of the band-limitedproportional-action controller. The overall frequency response function,G_(c)(s), now includes pure integral action,

$\frac{{\tau_{lead}s} + 1}{s},$up to frequency

${\omega = \frac{1}{\tau_{lead}}},$which has the effect of producing zero steady state error between thesense force and the balance force. The variable s represents the Laplacevariable.

Those skilled in the art will readily appreciate that the design of thepressure-regulating valves, e.g. pressure regulating valves 100 and 200,largely uncouples steady state and dynamic performance of the pressureregulation system. The selection of the diameter of sense piston 106 or206, and the diameter of first valve spool 110 or 210 in combinationwith the selection of a set-point of the second stage pressure regulatordetermine the steady state sense pressure. The additional sizing ofbypass orifice 140 or 240, balance pressure chamber 136 or 236, thesecond stage pressure regulator and first spring 130 or 230 (ifutilized) determine the natural frequency, damping ratio and lagcompensator time constants, but do not change the steady state sensepressure.

It is contemplated that the size parameters of sense lines 104 and 204,bypass orifices 140 and 240, first valve spools 110 and 210, sensepistons 106 and 206, second valve spools 112 and 212, first springs 130and 230, second springs 132 and 232, and first and second stageregulators can be selected in order to achieve a suitable regulatornatural frequency and damping ratio. While shown and described in theexemplary context of coolant and/or lubricant oil for generators, thoseskilled in the art will readily appreciate that valves in accordancewith this disclosure can be used in any other suitable application.

The methods and systems of the present disclosure, as described aboveand shown in the drawings, provide for pressure-regulating valves withsuperior properties including small or zero deviation of sense pressurefrom target value at steady state and tunable dynamic performance. Thedynamic performance can be tuned with respect to natural frequency anddamping ratio to provide stable operation that does not amplifyhydraulic resonance of the cooling system. While the apparatus andmethods of the subject disclosure have been shown and described withreference to preferred embodiments, those skilled in the art willreadily appreciate that changes and/or modifications may be made theretowithout departing from the spirit and scope of the subject disclosure.

What is claimed is:
 1. A pressure-regulating valve comprising: a valvesleeve including a first end and a second end defining a longitudinalaxis therebetween, and a bore axially aligned between the first andsecond ends; a sense line defined within the bore proximate the firstend; a sense piston mounted within the bore between the sense line andthe second end, configured to move along the longitudinal axis inresponse to pressure exerted by fluid in the sense line; a main chamberdefined within the bore between the sense piston and the second end,wherein the main chamber includes an supply port and a vent port,wherein the supply port and the vent port are in fluid communicationwith one another by way of the main chamber; a first valve spool mountedwithin the bore between the sense piston and the second end, wherein thefirst valve spool occludes a portion of the vent port to a variableextent to modulate a flow rate between the supply port and the ventport, and wherein the first valve spool is configured to move along thelongitudinal axis to modulate a flow rate in a fluid circuit forregulation of a sense pressure; a bypass line defined through the firstvalve spool; and a second valve spool mounted within the bore betweenthe first valve spool and the second end configured to move along thelongitudinal axis to modulate flow rate in the bypass line forregulation of a balance pressure.
 2. A pressure-regulating valve asrecited in claim 1, wherein the valve sleeve includes a first housingportion proximate the first end and a second housing portion proximatethe second end, wherein the sense piston and first valve spool aremounted in the first housing portion and the second valve spool ismounted in the second housing portion, and wherein the second housingportion is secured to the first housing portion with a mechanicalfastener.
 3. A pressure-regulating valve as recited in claim 1, furthercomprising a first spring mounted between the first valve spool and asecond housing portion proximate the second end of the valve sleeve,wherein the first spring is operatively connected to the first valvespool for biasing the first valve spool towards the first end of thevalve sleeve.
 4. A pressure-regulating valve as recited in claim 3,further comprising a second spring mounted within the bore between thesecond valve spool and the second end of the valve sleeve, wherein thesecond spring is operatively connected to the second valve spool forbiasing the second valve spool towards the first end of the valvesleeve.
 5. A pressure-regulating valve as recited in claim 1, whereinthe bypass line is defined between the sense line and a balance pressurechamber for fluid communication therebetween, wherein the balancepressure chamber is defined between the first valve spool and the secondvalve spool.
 6. A pressure-regulating valve as recited in claim 5,wherein the bypass line is defined through the sense piston and thefirst valve spool.
 7. A pressure-regulating valve comprising: a valvesleeve including a first end and a second end defining a longitudinalaxis therebetween, and a bore axially aligned between the first andsecond ends; a sense line defined within the bore proximate the firstend; a sense piston mounted within the bore between the sense line andthe second end, configured to move along the longitudinal axis inresponse to pressure exerted by fluid in the sense line; a main chamberdefined within the bore between the sense piston and the second end,wherein the main chamber includes an supply port and a vent port,wherein the supply port and the vent port are in fluid communicationwith one another by way of the main chamber; a first valve spool mountedwithin the bore between the sense piston and the second end, wherein thefirst valve spool occludes a portion of the vent port to a variableextent to modulate a flow rate between the supply port and the ventport, and wherein the first valve spool is configured to move along thelongitudinal axis to modulate a flow rate in a fluid circuit forregulation of a sense pressure; a bypass line defined between the senseline and a balance pressure chamber for fluid communicationtherebetween; a second valve spool mounted within the bore between thefirst valve spool and the second end configured to move along thelongitudinal axis to modulate flow rate in the bypass line forregulation of a balance pressure, wherein the balance pressure chamberis defined between the first valve spool and the second valve spool; anda bypass orifice within a portion of the bypass line in the sense pistonproximate to the sense line, wherein the bypass orifice is configured tosustain a pressure differential between the sense line and the balancepressure chamber and to meter flow through the bypass line.
 8. Apressure-regulating valve comprising: a valve sleeve including a firstend and a second end defining a longitudinal axis therebetween, and abore axially aligned between the first and second ends; a sense linedefined within the bore proximate the first end; a sense piston mountedwithin the bore between the sense line and the second end, configured tomove along the longitudinal axis in response to pressure exerted byfluid in the sense line; a main chamber defined within the bore betweenthe sense piston and the second end, wherein the main chamber includesan supply port and a vent port, wherein the supply port and the ventport are in fluid communication with one another by way of the mainchamber; a first valve spool mounted within the bore between the sensepiston and the second end, wherein the first valve spool occludes aportion of the vent port to a variable extent to modulate a flow ratebetween the supply port and the vent port, and wherein the first valvespool is configured to move along the longitudinal axis to modulate aflow rate in a fluid circuit for regulation of a sense pressure; abypass line defined between the sense line and a balance pressurechamber for fluid communication therebetween; a second valve spoolmounted within the bore between the first valve spool and the second endconfigured to move along the longitudinal axis to modulate flow rate inthe bypass line for regulation of a balance pressure, wherein thebalance pressure chamber is defined between the first valve spool andthe second valve spool; and a transfer tube between the sense piston anda first land portion of the first valve spool for connecting a firstportion of the bypass line in the sense piston with a second portion ofthe bypass line in the first valve spool.
 9. A pressure-regulating valveas recited in claim 1, wherein the main chamber is defined between firstand second land portions of the first valve spool.
 10. Apressure-regulating valve as recited in claim 9, wherein the bypass lineis defined between the main chamber and a balance pressure chamber forfluid communication therebetween, wherein the balance pressure chamberis defined between the first valve spool and the second valve spool. 11.A pressure-regulating valve as recited in claim 10, wherein the bypassline is defined through the first valve spool along the entire length ofthe first valve spool.
 12. A pressure-regulating valve as recited inclaim 10, further comprising a bypass orifice within a portion of thebypass line in the second land portion proximate the balance pressurechamber, wherein the bypass orifice is configured to sustain a pressuredifferential between the sense line and balance pressure chamber and tometer flow through the bypass line.
 13. A pressure-regulating valve asrecited in claim 1, further comprising a balance pressure chamberdefined between the first valve spool and the second valve spool,wherein the balance pressure chamber includes an inlet and an outlet,wherein the second valve spool occludes a portion of the outlet of thebalance pressure chamber to a variable extent to regulate pressurewithin the balance pressure chamber.
 14. A pressure-regulating valve asrecited in claim 1, further comprising a balance pressure chamberdefined between the first valve spool and the second valve spool forminga portion of a balance pressure circuit, wherein the balance pressurechamber is configured for continuous fluid flow between an inlet of thebalance pressure chamber and an outlet of the balance pressure chamberfor purging trapped air from the balance pressure circuit.
 15. Agenerator comprising: a housing; a rotor disposed in the housingconfigured to rotate and generate electricity; a fluid circuit includingan inlet port and an outlet port; and a pressure-regulating valveoperatively connected to the fluid circuit to modulate the flow of fluidthrough the fluid circuit, wherein the pressure-regulating valveincludes: a valve sleeve including a first end and a second end defininga longitudinal axis therebetween, and a bore axially aligned between thefirst and second ends; a sense line defined within the bore proximatethe first end, wherein the sense line is in fluid communication with thefluid circuit; a sense piston mounted within the bore between the senseline and the second end, configured to move along the longitudinal axisin response to pressure exerted by fluid in the sense line; a mainchamber defined within the bore between the sense piston and the secondend, wherein the main chamber includes a supply port and a vent port,wherein the supply port and vent port are in fluid communication with anoil pump disposed in the housing; a first valve spool mounted within thebore between the sense piston and the second end configured to movealong the longitudinal axis to modulate a flow rate in the fluid circuitfor regulation of a sense pressure; and a second valve spool mountedwithin the bore between the first valve spool and the second endconfigured to move along the longitudinal axis to modulate flow rate ina bypass line for regulation of a balance pressure, wherein a frequencyresponse of the pressure-regulating valve is configured to be tunablefor compatibility with a frequency response of the fluid circuit.